The invention is directed to an aqueous dispersion of a hydrophobic silica as well as to the process for its production.
For example from the Brunner German AS No. 1163784 there is known a hydrophobic silica and inter alia it is employed as an agent for increasing the pourability of fire-extinguishing powders. The entire disclosure of Brown is hereby incorporated by reference and relied upon.
For the use as filler in rubber it is desirable with special operating processes, as, e.g. in the production of rubber gloves to mix an aqueous latex emulsion with an aqueous dispersion of a hydrophobic silica.
Of course it is known to produce aqueous dispersions of pyrogenically produced hydrophilic silicas by dispersing this silica in pure water with addition of an alkaline acting material as, e.g., alkali hydroxide or waterglass solution (see Shutte German Pat. No. 16674601). However, the hydrophilic, pyrogenically produced silicas show completely different properties as fillers than the hydrophobic silicas.
From Brunner German Pat. No. 1467023 and related Schutte U.S. Pat. No. 3,393,155, it is furthermore known to mechanically mix in the ratio of 5:1 to 10:1 water with progenically produced silicon dioxide (silica) that has been modified with halosilane so that it contains a powdery, uniform system (so-called "dry-water phase"). In this process there is not attained the formation of a dispersion. (There is hereby incorporated by reference and relied upon the entire disclosure of Schutte U.S. Pat. No. 3,393,155.)
The problem of the present invention is the production of an aqueous dispersion of a hydrophobic silica.